1. Field of the Invention
The present invention relates to a CVD apparatus and its purging method, and more particularly, to the composition of a CVD apparatus that is able to shorten the time required for purging treatment after performing maintenance, and its purging method.
In addition, the present invention relates to a moisture monitoring apparatus that measures the moisture contained in corrosive gas in the process when performing epitaxial growth and so forth using corrosive gas on a silicon wafer arranged in, for example, a reactor, a semiconductor production apparatus equipped with said moisture monitoring apparatus, and a method for judging the maintenance times of semiconductor production apparatuses.
2. Description of the Related Art
CVD apparatuses are apparatuses used to grow a semiconductor film on a wafer by chemically reacting a semiconductor gas introduced into a reactor on the wafer. However, since it is not possible in principle to react all material gases on the wafer, by-products end up adhering to various locations on the inside walls of the reactor. These by-products have an effect during film growth in the form of particles and so forth. Since they hinder the formation of a high-quality film, it is necessary to perform cleaning work (maintenance) on the inside walls of the reactor.
In a CVD apparatus for growing thick films, for example, maintenance is required on the order of once every 3-4 days. However, since the apparatus is opened to the atmosphere and is cleaned with alcohol and so forth during maintenance, a large amount of air is taken into the reactor resulting in the adherence of moisture on the inside walls of the reactor.
If moisture is present in the atmosphere during growth of semiconductor films, it reacts with the semiconductor material gas resulting in the formation of metal impurities or the formation of particles that worsen the film quality. Consequently, following maintenance, it is necessary to purge the inside of the apparatus with high-purity nitrogen or other insert gas before growing films to lower the moisture concentration to an extent that does not have a detrimental effect on film quality.
However, since the inside of CVD apparatuses have an extremely complex shape, and the adsorption strength of water molecules is extremely high, considerable time is required for removing moisture after maintenance, which in turn has a significant effect on the operation rate of the apparatus.
In the past, various contrivances have been made to shorten the time required for apparatus maintenance, including purging, examples of which include vacuum purging, heated purging (baking), the use of hydrogen or a combination of these. However, since the conditions and combination of vacuum purging and baking are determined based on experience, it has been difficult to optimize the purging method.
In addition, the completion of purging is judged based on an evaluation of the quality of a film that is actually grown following a certain degree of purging. Consequently, material gas and time were wasted on growth until a film having product level quality was obtained. This is referred to as wasted epitaxial growth. Since the amount of time required for purging varies according to the usage history of the CVD apparatus and the degree to which maintenance has been performed, there were cases in which the number of cycles of wasted epitaxial growth increased considerably.
In recent years, epitaxial wafers, in which a single crystal silicon thin film (epitaxial layer) is vapor deposited at a prescribed impurity concentration on a silicon wafer having extremely low resistivity, are produced with an epitaxial crystal growth apparatus for use as silicon wafers for MOS devices. This apparatus performs epitaxial growth on a wafer by allowing a corrosive source gas to flow into a chamber in which a silicon wafer has been arranged. Furthermore, in this apparatus, etching of polysilicon adhered inside the chamber is also performed by a corrosive gas in the form of hydrogen chloride gas.
In addition, various CVD apparatuses that form a thin film on a wafer using corrosive gas, or etching devices for performing patterning, are used in LSI and other semiconductor production processes.
Although these semiconductor production apparatuses use corrosive gases such as ultra-high-purity hydrogen chloride gas and ammonia gas, if even a slight amount of moisture is present in this gas, there is increased susceptibility to the occurrence of corrosion of metal parts used in the apparatus (such as the inside of the process chamber, gas supply system and gas exhaust system), which is harmful because it causes contamination by metals (heavy metals) produced from these metal parts. In addition, moisture taken into the chamber reacts with by-products adhering to the chamber inside walls and exhaust line, which may also be the cause of particle formation. Consequently, although various countermeasures are employed to reduce moisture inside the process chamber,. it is difficult to completely remove all moisture. It is therefore necessary to periodically perform apparatus maintenance, namely opening up the process chamber and cleaning the members inside (quartz jigs, etc.). In the past, for example, maintenance times were judged based on the cumulative number of wafers processed in the case of single-wafer CVD apparatuses.
However, the above conventional method of judging maintenance times still has the problems indicated below. Namely, the amount of moisture actually introduced into the chamber each time maintenance is performed varies depending on the contents of work performed and the amount of time the chamber is opened during maintenance. Thus, in the case of judging maintenance times based on the cumulative number of wafers processed as has been done in the past, maintenance is performed for every fixed number of processing cycles regardless of the amount of moisture actually introduced into the chamber, and there was no guarantee that maintenance is performed at suitable times. For example, in the case an amount of moisture was introduced during the previous round of maintenance that is greater than the expected amount, there was the risk of high film quality not being obtained if processing is not performed until the prescribed cumulative number of wafers processed. In addition, in the case the amount of moisture introduced during the previous round of maintenance is comparatively low, maintenance ends up being performed earlier than the time when maintenance is actually required, leading to an excessively high number of maintenance cycles and decreased throughput.
In addition, it is also required to quantitatively analyze with high sensitivity the moisture contained in, corrosive gas inside the chamber in terms of reducing the moisture in the process chamber.
Known examples of moisture meters for measuring the moisture in a gas include the crystal oscillator method in which changes in the frequency of a crystal oscillator are measured, and the electrostatic capacitance method in which changes in electrostatic capacitance are measured by adsorbing moisture in a gas. However, since these moisture meters require direct contact with the gas, measurement was unable to be performed in the case of corrosive gases due to the corrosive nature of these gases.
Therefore, a laser moisture meter has been proposed in recent years, such as that described in Japanese Unexamined Patent Application, First Publication No. Hei 5-99845 and Japanese Unexamined Patent Application, First Publication No. Hei 11-183366, that uses infrared absorption spectrometry to measure trace amounts of impurities contained in gases using laser light. This laser moisture meter detects impurities such as moisture based on the intensity of the absorption wavelength by analyzing transmitted laser light when laser light having a prescribed wavelength is directed at a measurement cell while introducing corrosive gas into the measurement cell. Thus, there is no need to adsorb the corrosive gas and measurements can be performed quickly and with high sensitivity.
However, measurement means using the above moisture meter of the background art still have the problems indicated below. Namely, although a portion of the corrosive gas is introduced into the above moisture meter after passing through a sampling pipe after being heated inside a chamber, reaction by-products end up adhering and accumulating on the inside walls of the sampling pipe that leads to the moisture meter, resulting in the risk of obstruction of the sampling pipe. Consequently, it was difficult to use this moisture meter for constant measurement of moisture in corrosive gases during the process, namely for in situ monitoring.
Therefore, a first object of the present invention is to provide a CVD apparatus and its purging method that allows purging treatment after maintenance to be performed efficiently, makes it possible to accurately determine completion of purging treatment, shortens the time required for purging treatment, and makes it possible to quickly start up the CVD apparatus.
In addition, a second object of the present invention is to provide a method for judging maintenance times of semiconductor production apparatuses that is able to determine suitable maintenance times.
Moreover, a third object of the present invention is to provide a moisture monitoring apparatus and a semiconductor production apparatus equipped with said moisture monitoring apparatus that prevents obstruction of a pipe and allows measurement of moisture contained in corrosive gas even during processing.
In order to achieve the above first object, the CVD apparatus of the present invention comprises a CVD apparatus that supplies semiconductor material gas to a reactor (reaction chamber) in which a wafer is placed to form a semiconductor film on said wafer; wherein, together with connecting a material gas supply path that supplies said semiconductor material gas, an inert gas supply path that supplies inert gas for purging, and a high thermal conductivity gas supply path that supplies gas such as hydrogen or helium having a high coefficient of thermal conductivity that mixes with purge gas, to said reactor, a moisture meter that measures the amount of moisture in gas exhausted from the reactor, and a vacuum pump for evacuating the inside of the reactor, are provided.
In addition, in order to achieve the above first object, the purging method of the CVD apparatus of the present invention comprises a purging method of a CVD apparatus that supplies semiconductor material gas to a reactor (reaction chamber) in which a wafer is placed to form a semiconductor film on said wafer; wherein, a gas consisting of a mixture of a gas such as hydrogen or helium having a high coefficient of thermal conductivity and an inert gas, is used as the purge gas used during heated flow purging treatment in a purging treatment following maintenance, and the pumping of a vacuum inside the reaction chamber and the introduction of inert gas are repeated a plurality of times.
According to the CVD apparatus and purging method of a CVD apparatus of the present invention, purging treatment of the reactor can be performed efficiently, and timing of the start of film growth can be accurately determined. Therefore, the operating efficiency of the CVD apparatus can be improved and wasted epitaxial growth can be eliminated, thereby making it possible to reduce waste of material gas and time.
In order to achieve the above second object, the method for judging the maintenance times of semiconductor production apparatuses of the present invention comprises a method for judging the maintenance times of semiconductor production apparatuses that perform corrosive gas treatment in a reaction chamber by measuring the moisture concentration in the reaction chamber with a moisture meter connected to said reaction chamber when performing said corrosive gas treatment, and determining said maintenance times according to changes in said moisture concentration when corrosive gas treatment is performed repeatedly.
In this method for judging the maintenance times of semiconductor production apparatuses, since the moisture concentration in a reaction chamber is measured with a: moisture meter connected to the reaction chamber when performing corrosive gas treatment to determine maintenance times according to changes in moisture concentration when corrosive gas treatment is performed repeatedly, suitable maintenance times can be accurately judged since said moisture concentration changes according to the amount of moisture actually taken into the reaction chamber. Thus, in addition to being able to maintain the apparatus in a satisfactory state at all times, the number of times maintenance is performed can be reduced and maintenance intervals can be extended, making it possible to improve throughput.
In addition, it is preferable that the method for judging maintenance times of semiconductor production apparatuses of the present invention determine said maintenance times according to the cumulative amount of moisture by calculating the cumulative amount of moisture that has accumulated from the previous round of maintenance and been taken into said reaction chamber based on said change in moisture concentration.
Since maintenance times are determined according,to the cumulative amount of moisture as calculated from the change in moisture concentration in this method for judging maintenance times of semiconductor production apparatuses, the amount of moisture that is actually taken into the reaction chamber can be estimated accurately, thereby making it easy to judge suitable maintenance times.
Moreover, it is preferable that the method for judging maintenance times of semiconductor production apparatuses of the present invention measure the pressure inside the reaction chamber with a pressure gauge connected to said reaction chamber when performing said corrosive gas treatment, and determine said maintenance times according to said cumulative amount of moisture and the change in said pressure when corrosive gas treatment is performed repeatedly.
Since maintenance times are determined according to the change in pressure inside the reaction chamber and the cumulative amount of moisture in this method for judging maintenance times of semiconductor production apparatuses, even more suitable maintenance times can be determined Since the flow status of the pipe of the exhaust system, such as fluctuations in pressure that occur when the pipe is obstructed, can be detected from changes in pressure inside the reaction chamber, and this flow status can be taken into consideration along with moisture concentration.
In addition, it is preferable that the method for judging maintenance times of semiconductor production apparatuses of the present invention be a laser moisture meter in which said moisture meter directs laser light into a tubular cell. body connected to said reaction chamber and measures the absorption spectrum of the transmitted laser light.
In recent years, a laser moisture meter has been proposed in, for example, Japanese Unexamined Patent Application, First Publication No. Hei 5-99845 and Japanese Unexamined Patent Application, First Publication No. Hei 11-183366 that directs laser light into a tubular cell body connected to a process chamber and measures the absorption spectrum of the transmitted laser light as a means of measuring the moisture concentration in corrosive gases. Since this laser moisture meter is able to measure moisture concentration without making contact with corrosive gas, measurements can be made with high accuracy even in corrosive gas. Namely, since the above, method for judging maintenance times of semiconductor production apparatuses uses the above laser moisture meter for its moisture meter, moisture concentration in the reaction chamber can be measured accurately even while the process is n progress, thereby making it possible to determine maintenance times with high precision.
In order to achieve the above third object, the moisture monitoring apparatus of the present invention is a moisture monitoring apparatus equipped with a pipe of which one end is connected to a reaction chamber into which flows corrosive gas, and a moisture meter connected to the other end of said pipe that measures moisture contained in corrosive gas introduced from said reaction chamber, in which technology is employed that is at least provided with a pipe heating mechanism that heats said pipe.
Since this moisture monitoring apparatus is at least equipped with a pipe heating mechanism that heats a pipe, the pipe can be heated to a prescribed high temperature, enabling corrosive gas heated in the reaction chamber to flow while preventing the adhesion and deposition of reaction by-products in the pipe. Thus, obstruction of the pipe can be prevented enabling moisture to be measured constantly even while the process is in progress.
The above pipe heating mechanism can be in the form of a heating wire coiled around the outside of the above pipe in the above moisture monitoring apparatus.
Since the pipe heating mechanism in this moisture monitoring apparatus is equipped with a heating wire coiled around the outside of a pipe, the pipe can be heated with a simple configuration and the temperature of the pipe can be easily controlled by adjusting the current supplied to the eating wire.
Furthermore, the heat insulating and heat retention properties of this heating wire may be improved by covering the wire with a heat-resistant insulating material.
The above moisture meter in the above moisture monitoring apparatus can be a laser moisture meter that directs laser light into a tubular cell body connected to the other end of said pipe and measures the absorption spectrum of the transmitted laser light.
Since the moisture meter in this moisture monitoring apparatus is a laser moisture meter that directs laser light into a tubular cell body connected to the other end of said pipe and measures the absorption spectrum of the transmitted laser light, moisture can be quantitatively analyzed with high precision even in corrosive gas.
The above moisture meter in the above moisture monitoring apparatus may be equipped with a cell heating mechanism that heats the above tubular cell body.
Since the moisture meter in this moisture monitoring apparatus is equipped with a cell heating mechanism that heats the tubular cell body, the tubular cell body is also heated and the adhesion and deposition of reaction by-products inside the cell can be prevented, thereby enabling measurements to be made with high accuracy at all times. Thus, moisture can be quantitatively analyzed rapidly and with high sensitivity even during processing, and the correlation between the quality and conditions of corrosive gas crystal growth, thin film formation and etching and moisture content can be obtained with high accuracy, thereby making it possible to produce high-quality semiconductor wafers, semiconductor devices and other semiconductor apparatuses.
The above moisture meter in the above moisture monitoring apparatus may be composed such that the measurement sensitivity can be adjusted corresponding to the temperature of the above heated corrosive gas.
Some moisture meters are subject to variations in measurement sensitivity following a change in the temperature of the measured gas, and in the case of moisture meters: such as laser moisture meters that require a high level of measurement accuracy in particular, the effects of temperature cannot be ignored. However, since measurement sensitivity of the moisture meter is controlled corresponding to the temperature of the heated corrosive gas in this moisture monitoring apparatus, even if the temperature of corrosive gas being measured is changed by the pipe heating mechanism and so forth, moisture concentration can be measured with high precision according to the adjusted and corrected measurement sensitivity of the moisture meter.
In order to achieve the above third object, the semiconductor production apparatus of the present invention is a semiconductor production apparatus that allows corrosive gas to flow onto a wafer in a reaction chamber and reacts the corrosive gas on the surface of the wafer, and is equipped with the above moisture monitoring apparatus.
Since this semiconductor production apparatus is equipped with the above moisture monitoring apparatus, moisture can be quantitatively analyzed with high sensitivity even during processing, and the correlation between the conditions and quality of crystal growth, thin film formation and etching by corrosive gas and moisture content can be obtained at high accuracy.
This semiconductor production apparatus may be provided with a wafer transport system that transports the above: wafer through sealed space to the above reaction chamber, and may be provided with a moisture meter in said wafer transport system that measures moisture in said sealed space separate from the above moisture meter.
Since the wafer transport system of this semiconductor production apparatus is equipped with a moisture meter that measures moisture in a sealed space separate from the above moisture meter, moisture in sealed space of the wafer transport system can be measured and confirmed separately during transport of a wafer into a reaction chamber with a wafer transport system, thereby being able to prevent inadvertent inflow of moisture in said sealed space into the reaction chamber.